Velocity modulation tube



Patented Feb. 28, 1950 VELOCITY MODULATION TUBE lGeorges Goudet and Ren Musson-Genon, Paris, France, asslgnors to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application May 21, 1947, Serial No. 749,513 In France September 22, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires September 22, 1965 -4 Claims. (Cl. Z50-27.5)

The present invention relates to electron velocity modulation tubes. In velocity modulation tubes, particularly those comprising two resonant chambers, the electron beam traverses a space between the resonant chambers, which is called the drift space and which is in association with so-called buncher and catcher spaces, these being respectively in the nearest and furthest portions of the resonant chambers, with respect to the cathode. v

Since the Q factors of the resonant chambers are high, their selectivity is great and the band width is narrow, and this is sometimes a considerable drawback.

Besides, the power delivered by velocity modulation tubes, although appreciable in the range of very high frequencies, is relatively small.

One of the objects of the present invention is to increase the band width of velocity modulation tubes. Another object of the invention is to increase the power delivered by such tubes.

Another object of the present invention is to prolong the life of the cathodes of velocity modulation tubes.

According to one of the features of the present invention, the catcher space is of small size, and this permits the use of resonant chambers having a relatively low Q factor.

According to other features ofthe present invention, the drift space is of conical shape, the widest part of the electron beam being adjacent to the cathode, and the most concentrated part of the beam being at the catcher space.

Other features and advantages of the present invention will be found in the following description given with reference to the appended drawings in which:

Fig. 1 is a diagrammatic sectional view illustrating one example of a two-chamber velocity modulation tube incorporating features of the invention, and

Fig. 2 is a diagrammatic sectional View illustrating one example of the application of the invention to a single chamber velocity modulation tube of concentric type.

Fig. 1 shows the application of the invention to a velocity modulation tube having two resonant chambers. The cathode is shown at l. This cathode may be of appreciable size and have an annular emitting surface, for example as shown.

The so-called Wehnelt focussing electrode is shown at 2. The electron beam 3 enters the drift space of conical shape shown at 4. The electron beam accordingly assumes a conical form. as

shown in the drawing, with a maximum concentration point near the catcher space 5.

The first resonant chamber is shown at 6, and the second one at 1. The outlet tube of the electron beam is preferably flared as indicated at 9,

so as to prevent too many electrons from being picked up by the walls of the resonator 'l before reaching the anode l0.

The illustrated arrangement makes it possible to obtain at the catcher space 5 a very great concentration of current by purely electric means, without intervention of magnetic fields, and with a cathode having a low coeicient of emission per unit of surface. Suitable input and output terminals, not shown, would be associated with the resonators in Well known manner. Y

As mentioned above, one advantage of the arrangement of the present invention is thatit permits the obtaining of a greater band width by making it possible to employ a lower Q factor and therefore to have a higher resistance load so that greater power is derived from the tube.

Referring to the catcher space 5, this really constitutes the element of a resonating circuit in which the self-induction may be considered to be formed by the resonant chamber 1, and the condenser by the capacity between the two faces 8 and 9 of the catcher space 5.

The employment of a beam that is concentrated yat the catcher space 5 makes it possible to reduce this capacity by making the catcher space of smaller size, this capacity being substantially proportional to the geometrical dimensions at points 8 and 9.

In a velocity modulation tube, it is known that, for a given oscillation condition, the term in which Q represents the excess voltage coeilicient, C the capacity of the catcher space, and w the pulsation of the oscillations (2n-f), has to have a. certain relation with the impedance of the electron beam, defined as:

U being the applied voltage, and I the density of the electron beam.

By reducing the value of C through the use of a concentrated beam according to features of the invention, it is'possible, for the same frequency or oscillation condition, to reduce the excess voltage factor Q and consequently to increase the band width which. as is known. is

directly connected to the damping of the circuit, that is to the excess voltage coefiicient Q Indeed, theterrn p, v

has a value fixed by the Voltage and current" intensity conditions; consequently,w.if "C: V ref duced, the factor Q may be reduced in the same proportions, or the damping increased;

The means provided by thefinvention/mafke/it possible to obtain this result with c'athodeswh'ose coefficient of emission may be very small,` beoutwardly flared towards said electrodes.

l3. A velocity modulation tube comprising a fbuncherresonatoL- a'catcher resonator, a conical driftv 'tube-"between :said resonators, the walls of l bojtliovf ysaidresonators being provided with recause it becomes possible to gine them. aumore" considerable surface than would be :possible/by'.

using a parallel electron beam ,Onfthe.other hand, the use of a parallel beam wouldlnecessitate the use of a very active cathode of small size and consequently of short life.

Fig. 2 illustrates another example of embodimentadapted :to another type rof velocity `modulation tube having-a concentric structurefthatcomprisesian` outerpart 2D andaf'central, part 2i VThe.zrathode .is shown at 22, and the :electron beam passes into 'the channel 23- and through the drift space y24. The modulation or buncher space-is'atl,andthe-catcher spaceat 26. n

' The drift-space 24 is of conicalshape, with a relatively large` surfaceas it leavesqcathodefZZ andra-small one when it reaches'the ycatcher space 26.

.The .centralpart 2|Yis supported within the outer ,chamber 20 by means of securing' members 2". A

",The ysingle resonant chamber .is formed by :the concentric space .between the inner Vand-outer partsz and f2i..

This embodiment possesses the same advantages asthe. preceding one fromthe `view pointof damping. n

Although the invention haslbeen described for certainparticularexamples of embodiment', it is evident that it is by no means limited to the said exampl'eajand that they are capableoinumerous variants and modifications .without .departing iromits scope.

`What is claimedis':

1. A "velocity modulation tube comprising a cavity resonator, a conical drift "tube withinz'sad resonator', k"said/resonator having reentrant walls in'lmewith'said conical drift tube, said walls defining-a pair of oppositely'disposediopenings said entrant openings in line with said drift tube and spacediresp'ectivelyifrom the ends thereof to form .buncher and catcher spaces, said openings being 'ofvidiierentsze to cooperate respectively with the :.basle'anditheapex portions of said drift tube and means adjacent the opening in said buncher resvcna-tor"forprojecting a beam of electrons through said drift tube and said buncher and catcher spacestirr` the directiony fromfthe :,baseto i 'thef'apex ofv said"monica-ly tube. 1.4. A,A'rvelocity -.;-modulation. :tube -comprisingv :a

cavity .'resonatonfa .conical 'dri-ft tube supported. concentrically within :said resonator, `the Wall of said resonator A being provided with vreentrant openings: in .line wilfhsaidI conical ldrifttubegsaid openings being of diierent -fsizet'o Vcooperate re speictively with the .base-andthe apexportiens of. said drift tube and means adjacent one crsaidy openings for projecting al :beamyzo electrons throughsaid openingsand.` said drifttubeg-i-n the. directonfromf vthe `base .toz theo-apexY ofsaid conicai tube.

GEORGES GOUDET.

REN r`'1v1-Ussola-:eration REEERENCES ',GITED` The. following 'reiferences are .of record. in the. le `oflthis pat-ent: y'

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